1. Field of the Invention
The present invention relates to a magnetic sensor switch that is operable in response to external magnetism to turn its contacts on and off, and more particularly, to a magnetic sensor switch of the type that comprises a magnetic sensor responsive to approach of a magnet, electrical contacts, and a driving member for transmitting the movement of the magnetic sensor to the electrical contacts, and is operable in response to the movement of the magnetic sensor to turn the electrical contacts on and off.
2. Description of the Related Art
As is disclosed in Japanese Patent Application Public Disclosure No. hei 6-347559 (347559/1994), for example, a magnetic sensor consisting of a combination of a permanent magnet and a reed switch responsive to magnetism has been heretofore known. As shown in FIG. 1, the magnetic sensor disclosed in the Japanese Patent Application Public Disclosure No. 347559/1994 comprises an elongated cylindrical case 71 made of a non-magnetic material, a reed switch 75 disposed in the interior of the case 71 generally in the center thereof, a columnar permanent magnet 73 mounted in the interior of the case 71 at the forward end (left-hand end as viewed in the drawing), a magnetic plate 87 attached to the outer side wall of the enclosure (glass tube in this example) 77 of the reed switch 75, and a magnetism adjusting permanent magnet 74 mounted at the peripheral area of the glass tube 77 adjacent one end thereof. The two permanent magnets 73 and 74 positioned on the opposite sides of the reed switch 75 are configured such that the opposing sides of the magnets 73 and 74 have the same magnetic polarity. In this example, the magnetic polarities of the opposing sides (the reed switch side) of the two magnets 73 and 74 are set both to be the S magnetic pole.
The reed switch 75 is positioned generally in the center of the case 71 by two spaced rings 76 and 78 both of which are made of heat resistant, electrical insulating material. The root portion of the case 71 is mounted to a sensor mounting base 95 by means of a bushing 91 made of rubber. Lead wires 96 and 99 leading out from reeds 93 and 94, both being made of a magnetic material, of the reed switch 75 are connected to suitable heat-resistant, insulated wires 89 and 90, respectively, that extend to the outside through the root portion of the case 71. As is well known, the forward ends of these reeds 93 and 94 comprise contact portions 79 acting as electrical contacts.
Next, the operation of the magnetic sensor constructed as described above will be briefly explained with reference to FIGS. 2 and 3. FIG. 2 shows magnetic lines of force generated from the magnetic sensor shown in FIG. 1 when the magnetic sensor is in the standby state in which there is no magnetic substance (object) or magnet in the vicinity around the sensor. From FIG. 2, it will be appreciated that there is a very weak magnetic field produced in the vicinity of the contact portions 79 of the reed switch 75. The distribution of the magnetic lines of force generated from the magnetic sensor during this standby state may be preliminarily adjusted by moving the magnetism adjusting permanent magnet 74 longitudinally of the case 71. When the magnetic field applied in the vicinity of the contact portions 79 of the reed switch 75 is relatively weak as shown in FIG. 2, the contact portions 79 remain open, and hence the reed switch 75 is in the off state.
As a magnetic substance or magnet approaches the vicinity of the magnetic sensor in the standby state, the magnetic field applied to the reed switch 75 changes. FIG. 3 shows magnetic lines of force generated from the magnetic sensor when two iron balls 97 and 98 being magnetic material approach the vicinity of the forward end of the reed switch 75. As is apparent from FIG. 3, the magnetic field in the vicinity of the contact portions 79 of the reed switch 75 is significantly intensified as compared with that in the standby state. As a result, the reeds 93 and 94 made of a magnetic material magnetically attract and contact each other, and hence the contact portions 79 go to on state. Further, the detailed construction, structure and operation of this magnetic sensor are disclosed in Japanese Patent Application Public Disclosure No. 347559/1994. Accordingly, further description thereof is omitted for purposes of convenience.
This magnetic sensor includes the magnetic plate 87 disposed in the vicinity of the contact portions 79 and the magnetism adjusting permanent magnet 74 positioned at the one end of the reed switch 75 near the base of the case, in addition to the permanent magnet 73, so that the magnetic field produced by the permanent magnet 73 in the vicinity of the contact portions 79 of the reed switch 75 may be adjusted by the magnetic plate 87 and the magnetism adjusting permanent magnet 74 to control the dynamic or operating sensitivity of the contact portions 79 of the reed switch 75.
As discussed above, this magnetic sensor is configured such that the magnetic field produced mainly by the permanent magnet 73 is applied directly to the reed switch 75 and the contact portions 79 of the reed switch 75 is controlled to turn on and off by that the applied magnetic field is varied by a magnetic substance or a magnet approaching the magnetic sensor. Otherwise stated, this is a magnetic switch of the type in which the magnetic field applied directly to the reed switch 75 is varied by an approaching magnetic substance or magnet whereby the opposing reeds 93 and 94 of the reed switch 75 are attracted to each other so that the contact portions 79 are controlled to the on position.
It is thus to be understood that the switch of this magnetic sensor would not be turned on unless there occurs a change in the magnetic field to some extent. Further, this magnetic sensor will be turned on, irrespective of the polarity of a magnet approaching the magnetic sensor and even if the approaching object is a magnetic substance or object rather than a magnet. For this reason, the illustrated prior art magnetic sensor can not be used in applications where the switch of the magnetic sensor is required to be turned on and off only when it is approached by a particular magnetic pole of a magnet.
In addition, because the prior art magnetic sensor as described above utilizes a reed switch, it has the disadvantages that the cost of manufacture is correspondingly increased and moreover, in the event of failure of the contact portions, the entire reed switch must be replaced, which leads to an increase in the maintenance cost.
An object of the present invention is to provide a magnetic sensor switch that does not utilize a switch having its contact portions to which a magnetic field is directly applied such as a reed switch.
Another object of the present invention is to provide a magnetic sensor switch in which its magnetic sensor causes its electrical switch to turn on and off in response to the approach of a particular magnetic pole of a magnet to the magnetic sensor.
In order to accomplish the foregoing objects, in one aspect of the present invention, a magnetic sensor switch is provided which comprises: an elongated magnetic sensor having magnetic poles contrary to each other at opposite ends thereof and mounted for rotation through predetermined angles in clockwise and counter-clockwise directions; a movable contact piece including a pair of contact blades; a pair of fixed contact pieces located in opposition to the pair of contact blades of the movable contact piece, respectively; a common contact piece electrically connected to the movable contact piece; a driving member transmitting the movement of the magnetic sensor to the movable contact piece; an auxiliary magnet located on a longitudinal extension line of the magnetic sensor and mounted such that it can be moved toward and away from one of the magnetic poles of the magnetic sensor; a first magnetic member located at a predetermined position outside of the rotating radius of the magnetic sensor and in the vicinity of the one magnetic pole; and a second magnetic member located at a predetermined position outside of the rotating radius of the magnetic sensor and in the vicinity of the other magnetic pole.
In one preferred embodiment, the aforesaid magnetic sensor is a generally cylindrical member comprising a cylindrical central body made of a magnetic substance, a first magnet affixed to the cylindrical central body at one of the opposite ends thereof, and a second magnet affixed to the cylindrical central body at the other of the opposite ends thereof; the aforesaid driving member comprises a movable contact piece driving section in the form of an elongated plate, and an actuating section formed integrally with the movable contact piece driving section and extending upwardly from one lateral side edge of the middle portion of the movable contact piece driving section; the aforesaid movable contact piece comprises an elongated electrically conductive plate-like member of a rectangular shape in a plan view, a tongue formed transversely in the central portion of the plate-like member, first and second contact blades formed in the longitudinal direction of the plate-like member in the opposite side regions adjoining the central portion of the plate-like member and extending in the opposite directions to each other, and generally circular depending portions depending from the opposite side edges of the central portion of the plate-like member; each of the aforesaid fixed contact pieces comprises a contact portion adapted to contact with the corresponding contact blade of the movable contact piece and a terminal portion formed integrally with and folded from the contact portion; and the aforesaid common contact piece comprises an elongated plate-like contact portion and a common terminal portion formed integrally with and folded from the contact portion, the contact portion of the common contact piece being formed with through-holes into which rotary shafts for rotatably supporting the magnetic sensor, the driving member, and the movable contact piece should be inserted, respectively.
The aforesaid magnetic sensor may be a generally cylindrical magnet having N magnetic pole at one of the opposite ends thereof and S magnetic pole at the other of the opposite ends thereof.
In addition, the aforesaid auxiliary magnet acts such that it provides an attracting force and a repulsive force to the one magnetic pole of the magnetic sensor to rotate the magnetic sensor through the predetermined angle in one direction, thereby to hold the magnetic sensor in standby position in which it is stationary at an inclined position tilted from the horizontal position, and the aforesaid first and second magnetic members act to provide attracting forces to the corresponding magnetic poles of the magnetic sensor thereby to impart an instantaneous snapping force to the magnetic sensor when the magnetic sensor rotates in a reverse direction.
With the construction of the present invention described above, since the provision of the first and second magnetic members adds a clicking action to the magnetic sensor, the rotating movement of the magnetic sensor may be instantaneously effected when it is reversed thereby to enable the instantaneous changeover of the switch. On top of that, fine adjustment of the distance between the magnetic sensor switch and an external magnet that the switch can detect the approach of the external magnet can be carried out, and hence it is possible to enhance the reliability of the magnetic sensor switch. In addition, because this magnetic sensor switch does not utilize a switch such as a reed switch having its contact portions to which a magnetic field is directly applied, the cost of manufacture can be reduced, and on top of that the maintenance cost can also be reduced.